Telephone system



Nov, 17, 1931.

A. B. STERN TELEPHONE'SYSTEM Filed Feb. '7, 1930 3 Sheets-Sheet l/NVENTUR A. B. STERN NOV. 17, 1931. A, B, STERN 1,831,931

TELEIHONE SYSTEM Filed Feb. 7. 1950 3 Sheets-5h66?, 2

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/VENTUR A. EIERN Arm/wav A. B. STERN TELEPHONE SYSTEM Filed Fen 7, 195oMSM.

Patented Nov. 17, 1931 UNITED STATES PATENT ort-'ice ARTHUR B. STERNQOFFANWOOD, NEW' JERSEY, ASSIGNOR TO .AMERICAN TELEPHONE Y .AND TELEGRAPHCOMPANY, A. CORPORATION 0F YORK i TELEPHONE SYSTEM Application filedFebruary 7, 1930. Serial No. 426,@4.

p This invention relates to telephone systems and particularly tomachine switching systems.

The object of the inventionl is to improve 5 service from a centraloffice to private branch exchanges by enabling the increase of lines toprivate branch exchanges without disturbing existing facilities forhandling suchtrafic. V

Heretofore, systems have been provided in which connections from acalling line have been extended over automatic switches in one exchangeto mark a certain pointor terminal and then, due to this marking, anidle trunk l5 leading to a desired exchange has been connected to thecalling line over another path. A feature of this invention is a systemof this general character inY which a connection may be established overswitches to mark sets of terminals where each'set represents a certa-ingroupy of lines outgoing from' an exchange and in which, due to thismarking, auxiliar)7 switches are controlled toextend A the connection toan idle line in the marked a group.

Another feature is a system in which each set of terminals representinga group of lines is variously connected to currentsources to establishcharacteristic potential conditions 5 on these terminals. Theseconditions are employed for' the guiding or" the auxiliary switches toestablish connections to the marked groups ofV outgoing lines and tocause said switches to hunt for idle lines in said ""5 group and connectthem when found to callinv' lines. y

his invention has been illustrated in the accompanying drawings in whichFig. 1 shows the switches for marking the connection to be establishedand Figs. 2 and 3' show the circuits of two line selecting auxiliaryswitches. v i

In establishing a connection to an idle trunk in a group leading to adistant private branch exchange, the connection is first set up over theincoming'selector 1 and the final selector' 2, toa `cross-connectingframe 3 where a set of terminals representing the desired group oflines'is selected. These sets of terminals'arev provided with variouselec'- `matic telephone system.

trical characteristic potential conditions which serve toguide theAauxiliary switches, such as the auxiliary incoming selector 200 ot Fig.2 and the auxiliary final selector 300 v of Fig. 3, to the desi-redgroup of trunks out'- 65 going to a distant oiiice. All of theseswitches may be ofany well known type employed in panel type automaticsystems and in general the circuit arrangements for con'- trolling themmay also be of any well known type,lsuch for example as-'are disclosed'in the `Patent No. 1,395,977, to Stearn etal., ofNovember'LlQQl'." Theoperation of these switches to select a connection will therefore not bedescribed inthesucceeding text in any vfurther detail than is necessaryfor theffull understanding of the application of the present inventiontoa standard panel type auto- If it is now assumed that in setting up aconnection of this kind guiding impulses have been received overline l()andthe incoming selector land the final selector 2 have been actuated toselect-for example the set of terminals 11, this selection determines'the desired group of outgoing lines. The electrical conditions on thevarious sets of terminals at the cross-connecting frame 3, that guidesthe selections may be arranged as follows; The sleeve terminals may beconnected to ground through various resistances andv the resistancebetween a terminal and Vzo 4ground determinesI the brush selection inthe auxiliary incoming. selector Q00. This resistance may be inserted asshown at 12 between cross-connecting bars which are then connected tothe sleeve terminalsv accordance with a predetermined plan orarrangement of terminals on the nal selector. The tip and ring terminalsmay be connected either to groundor battery through variousresistances.v The polarity of the current on the ring terminaldetermines the group selection vin. the auxiliary incoming selector Q0()and the resistance inserted between the ground or battery on the ringterminal determines the brush selection in the auxiliary iinal selector300. The resistances for these purposes may be connected as shown at 13between the source and the cross-connecting 100 bars for the terminalswhich are connected to these bars as desired. The polarity applied tothe tip terminal determines whether the desired group of trunks is inthe upper or lower half of an auxiliary inal selector bank and theresistance on the tip terminal determines which of the five groups inthe selected half is the one over which hunting for an idle trunk 'shalltake place. The various combinations 'of conditions on the terminals atthe iinal selector 2 may be as follows: The sleeve terminals may beconnected to ground directly or through the succeeding resistances asshown at 12. The combinations of conditions on the tip and ringterminals may be as follows: ground on the ring and battery on the tipeither directly or through resistances as exemplified at 13; ground onthe ring and ground on the tip either directly or through resistances;battery on the ring and battery on the tip either directly or throughresistances, or battery on the ring and ground on the tip eitherdirectly or through resistances.

The arrangement of terminals at the auxiliary selectors may be asfollows, although it should bel understood that any other suitablearrangement may be made. In the auxiliary incoming selectors the banksmay contain 500 sets of terminals dividedl in 5 banks of 100 sets each.These banks may be selected by the brush selection, to wit, by thetripping ofA one out of five sets of brushes. The next selection will bethat of the lower or upper half of the determined bank of sets ofterminals and the trunk hunting for an idle auxiliary incoming selectormay therefore take place over a group of 50 sets of terminals with eachset ofterminals connecting to an auxiliary lfinal selector. VIn theauxiliary final selectors the banks may also contain- 500 sets ofterminals divided in 5 banks of 100 sets each. These banks may beselected by the brush selection through the tripping of one out of 5sets of brushes. The next selection will be that of the loweror upperhalf of 50 Asets of terminals each in thev determined bank, while thesucceedingselection will be one out of five groups of 10 sets ofterminals each and the hunting may take `place over the selected groupof 10 sets of terminals for an idle trunk leading to the desired privateAbranch exchange. Y

lt is assumed that the connection has been established to the terminals11, the selecto-rs 1 and 2 will have their respective sequence switches15 and 16 located in positions 8 and 6 respectively.y Vith sequenceswitch 1S in position 6, a circuit is now established for the operationof relay 17 from battery, windlngV of' this relay, sequence switch caniy18 Yover the sleeve brush and terminal to ground at 12. Relay 17 inoperating closes a circuit through sequence switch cam 2() for theadvancing of the sequence switch to position 15. The sequence switchwill now remain in this positio-n until the switch is released. Relay 17will also remain in operated position until the switch is releasedthrough a circuit over cam 18 to ground at the left hand arn'iature andfront Contact oi relay 17. It should be noted that when sequence switchcam 21 passes from 6 to (3% after the operation of relay 17, aconnection from battery through the right-hand armature and frontContact of relay 17 is momentarily extended over the sleeve conductorleading to the sleeve terminal of the incoming selector 1. lVhen thesequence switch passes into 7 and to position 18, the sleeve brush ofthe final selector 2 is connected through to the sleeve terminal ofselector 1, sothat the ground at 12 will then be connected through tothe incoming selector 1. The tip and ring conductors are also connectedthrough to the incoming selector when position 15 is reached by meane oflcams 22 and 23.

This momentary connection to battery for the sleeve conductor to theincoming selector l cause the operation of relay 25 over a circuit fromthis battery and the sleeve connection, through the sequence switch cam.2G position 8, winding of relay 25 to ground. Relay 25 in operatingcloses a connection to ground at its left-hand armature and frontcontact and cam 28 to advance the sequence switch 15 to position 17, inwhich position the switch will remain until the connection is released.Relay 25V closes a locking circuit for itselt to battery over cam 26.Relay 25 also prepares a circuit for the operation of relay 29 whichcauses the talking connection for the incoming line 10 over therepeating coil 30 to be disconnected from the auxiliary switches. Thiscircuit is closed as hereinafter described when the auxiliary incomingselector 200 has been seized. In this position thev tip and ring andsleeve conductors from the final selector are now extended through i"cams 32, 33 and 34 respectively, to conductors 35 leading to theauxiliary switches and the electrical conditions encountered at terminals 11 will now control the auxiliary switches to lll/O select thedesired group of trunk and hunt for and connect the incoming line 10 toan idle trunk in a manner to be hereinafter dcscribed.

Conductors 35 extend through switch 201 to the auxiliary incoming switch200. Switch 201 has merely been indicated inL diagrammatic form as itsuse is not essential to the full understanding of this invention. It maybe employed for automatically associating a common equipment ofauxiliary incoming and iinal switches wit-h lines such as 10 for examplein small exchanges where it would not be economical to provideindependent auxiliary switches for each incoming line as would be thecase in larger exchanges. Regardless of Whether this switch is used ornot the first eiiect atte-r the conductors 35 have been connected to theauxiliary incoming switch 200 will be that relay 29 is operated frombattery at relay 250 and also that the ground at 12 on the sleeveconductor will cause the operation of relay 202 overv a circuit frombattery winding of this relay, cam 203 in position 1, to the sleeveconductor over switches 1 and 2 to ground at 12. Relay 202 in operatingcloses a circuit at its right-hand armature and front Contact for theoperation of sequence switch to cause it to advance to position 2. In

this position relay 202 isreleased and the circuit. closed for the updrive magnet 204 to advance the4 brushes 205 of selector' 200 for brushselection. In position 2 a connection is established for relay 206 overcam 207 to the .brush selectingv commutators 209. The

brush selection is controlled by the condition on the sleeve conductoras determined at 12. Relay 206 is marginal and operates only when a.condition hasl been established whereby only four of the resistances at12 or at 208 or at both these points are included in the sleeveconductor circuit. It, asL shown in Fig. 1, the sleeve circuit isconnected directly to ground at 12, relay 206 will operate through allfour of the resistances at 208 assoon as the brushes210ioicommutat'or209 have advanced to connect with the commutatorl segment2111. On the other hand, if the sleeve circuit at 12 were groundedthrough the lirst or one resistance only thereatyrelay 206 will notoperate until the first resistancesA of the group `at'208 have beeneliminated. This takes place when the brushes 210 have advanced toconnect with the commutator segment 212. Ina similar manner if thesleeve circuit is connected through succeeding resistances at l12, relay206 will not operate until the'corresponding resistances in group 208have been eliminated by the brushes 210 advanced to the correspondingcommutator segment in the group 209. When therefore relay 206 doesoperate a circuit is completed from ground at its armature and frontcontact througl'l cam 214 for advancing the sequenceswitch 203 toposition 3. In this position relay 206'is'released bythe opening of thecircuit therefor at cam 207 and the up-drive magnet 202 i's alsoreleasedto stop the upward movement of the switch. In position 3 the tripAmagnet 216 isf operated over cam 217 to trip the proper set of brushesdetermined by the distance'traveled by the selector sha-tt'in a mannerwell known in the art. In this particular case it will be the iirst setof brushes so that selection will take place in the first of the fivebanks of terminals in Vthis selector. Vith relay 206 released. a circuitWill now be completed for advancing sequence switch 203 to position 4 bya circuit from ground at the armature and back Vcontact of relay 206through cam 214. With the sequence switch in position 4the operations ofthe circuits from this time on will be controlled by the conditions onthe tip and ring terminals at 11.

The next controlled movement of the incoming auxiliary selector will bethe selec- Z4 tion ofV the upper or lower half of the terminals in theselective bank. The condition on the ring terminal at 11 will nowdetermine this selecting movement of the auxiliary incoming selector200. If there is battery on the tip conductor the upper half will beselected and with ground on the tip conductor the lower half will beselected. With battery connected to the tip conductor as shown at 13 theupper half will be selected and in this case it will be observed thatwhile the sequence switch passed through position 31/2 into position 4relay 221 operated over a circuit as follows. Battery at 13 over thering conductor, cam 222 in position 31/2, lett-hand armature and backcontact and winding of relay 221, cam 223 in position 31/2, to ground.Relay 221 in-operating provides a locking circuit for itself frombattery at cam 225 independent of the battery on the ring conductor at13. A'circuit is now closed at the Vouter right-hand armature and frontcontact of relay 221 for reclosing the circuit of the up-drive magnet204 through cam 226. The up-drive'magnet will now again drive thebrushes upward and thereby cause the irst set of brushes to betrippedand when the brushes'have been advanced half wayup the selectedbank the brush of the commutator 229 connects this commutator to ground.IVhen this takes place a circuit is established for advancing of thesequence `switch from position 4 into position 6 over .cam 214,positions 4and 5. Relay 221-is now released as its locking circuit overcamV 225 A is open when. the sequence switch leaves position 4. Theup-drive magnet 204 is therefore stoppedwhen the sequence switch leavesposition 4.

In position 51/2 relay 230 is operated over a circuit through itsleft-handl winding and cam 231. In position 51/3 to 6, relay 230l isheld operated over a circuit from battery through the left-hand windingof this relay, cam 23.1, commutator 232 to ground at the brush for thissegment'. The up-drive magnet 204 is now again operated over a circuitcompleted through cam 226, position 6,`left hand armature and frontcontact of relay 230 to ground. Relay 230 is now held operated throughits right-hand winding to a ground over cam 234 encountered over thesleeve brush from the sleeve terminals of busy trunks leading to` busyfinal selectors. As stated relay 230 is lalso held operated over cam'231bythe ground ou the commutator 232. These ground connections, however,alternate tol hold the relay 230y operated. Then therefore an idle trunkis found identitled by the absence ofi the ground on` the les sleeveterminal, the relay 230 releases and opens the circuit of the up-drivemagnet 204. The limiting movement of the selector 200 is thereby stoppedand the corresponding idle final selector seized. A busy ground isimmediately placed on the sleeve terminal Y of this selector from theleft-hand armature and back contact of relay 230 through cam 234 inorder to guard this trunk and associated selector against seizure byanother auX- iliary incomingselector. The release of relay 230 alsocloses a circuit for the operation of relay 235 over a circuit frombattery, winding of this relay, cams 207 and 214 in position 6, toground at the left-hand armature and back contact of relay 230. Thesequence switch 203 is also advanced by the release of relay 230 toposition 7 from a circuit established over cam 214 to this ground at theleft-hand armature and back contact of relay 230. Sequence switch 203 isthen advanced to position 8 over cam 214 to the ground at the commutator229.

It should be observed at this time that in case the ring conductor hadbeen connected to ground instead of to battery as shown at 13,relay 221would not have operated until the sequence switch 203 had passed intoposition 41/2 as the battery connection would not have been completed atcam 223 until position 41/2 had been reached. The sequence switch 203would therefore be passed into position 5 from position 4, due to thisrelay failing to operate at position 31/2, by a circuit closed to groundtherefor at the inner right-hand armature and back contact of relay 221and cam 236. In position 5, with relay 221 operated, a circuit is closedfor advancing the sequence switch to position 6 from ground at the outerright-hand armature and front contact of relay 221 and cams 226 and 214.The 11p-drive magnet 204 will therefore not in this case be operated inposition 4 and consequently the hunting will take place in the lowerhalf of the selected group'of terminals. The operation of the circuitsin the selector 200 are the same as hereinbefore described in connectionwith the hunting for an idle trunk to an idle final selector. The onlyeX- ception and an important one is that the sequence switch 203 is onlyadvanced to the position 7 when trunk hunting ceases and relay 230releases. This is due to the fact that there will be no connection tovground at the commutator for the sequence switch in position 7 as thelower half of the bank of terminals was selected in this case.

Vith the sequence switch in position 8, as hereinbefore described whenthe upper half of the bank was selected, relay 235 releases and aconnection is now closed to complete. a loop for the tip and ringconductors over cams 237 and 222 towards the auxiliary iinal selector300. This loop extends over cams 303 and 304 in position 1 to batteryand ground,

with the tip connection completed through the winding of relay 238 andthe ring connection completed through the winding of relay 306. Relays238 and 306 operate in this circuit.

The operation of relay 306 closes a circuit for sequence switch 308 overcam 309, posi- .tions 1 to 5. It will be observed however that thesequence switch will be stopped in position 3 as the release of relay306 occurs before the switch reaches this position, as will hereinafterbe described. Relay 306 is locked through its own left-hand armature andfront contact over the ring and tip conductors through the loop at theincoming selector vto ground at cam 303 at the succeeding positions andbetween the positions it will be locked directly to ground at cam 310.Due to the grounding of the ring conductor between the positions by cam310, relay 238 will be alternately shunted and thus caused toalternately release and operate as the sequence switch 308 passes fromone position vto another. This alternate operation and release of relay238 is recorded by relays 239, 240 and 241 as follows. On the rstoperation of relay 238, relay 239 operates and locks to battery at cam203. At the release of relay 238, relay 241 operates and locks to groundfrom battery at cam 203. At the neXt operation of relay 238 relay 240operates `and locks to cam 203. When relays239, 240 and 241 are operatedand on the next release of relay 238 relay 235 will operate over anobvious circuit and sequence switch 203 will be advanced to position 9over a circuit through cams y214 and 207 iii-position 8, right-handarmature and front contact of relay 240, left-hand armature and-'frontcontact of relay 239 to ground at the right-hand armature and backcontact of relay 238. This operation of the sequence switch causes therelease of relays 239, 240 and 241 and the release of relay 240 causesthe release of relay 235. The tip and ring conductors are now extendedthrough to the final selector over cams 237 and 222. As these effectsarefproduced by the second release of relay 238 sequence switch 308 willstop in position 3. This is due to the fact that on the operation ofrelay 235 the locking circuit for relay 306 is opened and is not againclosed as the loop circuit through the incoming selector to ground atcam 303 will now be opened. Relay 306 in releasing opens the circuit forsequence switch 308 and with the switch in position 3 the final selectoris in condition for brush selecting operation with battery on the ringconductor.

The operation of the final auxiliary selector will now bedescribed'imder conditions where there is a battery connection on thering at the terminals 11. With the sequence switch in position 3 andrelay 306 released the up-drive magnet 310 will be operated over acircuit from battery winding of this magnet, cam 311 in 'position 3,right-hand armature and back contact of relay 306 to ground. Dependingnow on the resistance condition at the cross connecting frame on thering conductor, the relay 312 will operate when the resist-anceconditions have been met in the circuit completed through the commutator313 in the same manner as the conditions weresatisfied in the commutator209 auxiliary incoming selected circuit. That is, a circuit will beestablished for rela-y312 from the battery supplied over the ringconductor from 13 through cam .304 in position 3, winding of relay 312,cam 314 inposition 3, resistances at 315, one of brushes 316, commutator317, cam 318 in position 3, to ground.` As the ring terminal at 13 isconnected directly to battery, the relay 312 will operate as soon as thebrushes have been advanced to connect with the commutator segment 319,thus selecting the first set ofbrushes to be tripped in the switch.Relay 312 in operating closes an obvious circuit for the operation ofrelay 320v over Vcam 309, positions 3 to 5. Relay 320 locks through itsown armature and front contact and the sequenceswitch 308 is advanced toposition 6. When position y6 has been reached relay 320 is released bytheopening of the circuit therefor 4at cam 309. It should be noted thatrelay 312 releases as soon as the sequence ,switch left position 3asvthe circuit `therefor is open at cam 314 after position 3. Theup-drive magnet is also stopped after position 3 by 4the opening of thecircuit therefor at cani 311. lThetrip magnet 322 is operated over cam324 in position 6 to be ready to trip the' first set of brushes when thenext 11p-drive loccurs and the sequence switch 308 is advanced on `therelease of relay '320 to position 7 from a circuit completed at thearmature and back 'contact of this relay and cam309 in position 6. Inposition 7, the 11p-drive magnet 310 is again energized through acircuit completed through cani'324.

If on the other hand the .ring terminal at v 11 had been connected toground instead of the battery it will be remembered that the sequenceswitch 20.3 of selector 200 will remain in position 7 after theselections have been completed in this selector, Consequently when theloop circuit isV closed to selector 300 and when the cam 310 causesthealternate operation and release of relayl238, the control by relays239, 241, 240 and 235 over the selector 300 will be different. uIn thiscase when relay 235 operates the sequence switch 203 will be advanced'from position 7` to position 8 over the obvious circuit through cam214. This causes the release of relays 239, 241,240 and 235, but as thesequence switch is `only in position 8 the loop circuit to selector 300will be closed va second time. Consequently relay 306 will not bereleased at position 3 but maintain the circuit for the i sequencelswitch 308 to cause it tocontinue to position 5. Relay 238 willtherefore againrbe alternately operated and released under control ofcam 310 and the cycle of operation of relay 239, 241, 240 and 235repeated a second time. At the end of the second cycle of operation thesequence switch 203 will be ladvanced to the position 9 as hereinbeforedescribed and with the sequence switch 308 in position 5. The up-drivemagnet 310 will now be operated in the same manner asbefore, but relay312 operates in this case from battery supplied at the cam 318 inpositiony 5, through commutator segment 317, brushes 316, thecommutators in the group 313, through resistances 315, cam 314, windingof relay 312, cam 304, ring conductor to ground at the cross connectingfra-ine. Depending on the resistance conditions encountered at 13 therelay 312 will operate to select the proper set of brushes to betripped. Relay 312 closes the circuit for relay 320, which relay inoperatingcauses the sequence switch to advance to position 6 and stopthe updrive magnet 310. When this position is reached the trip magnet322 is ope-rated in position 6 and on the release of relay 320 thesequence switch is advanced to position'7.

The selection of the upper orlower group of terminals in the groupselectedby the tripping brushes will now take place and if there isbattery connected on the tip at the cross connecting frame, the effectwill be that the selection will take place in the upper part of the bankinstead of the lower part. This is taken care of entirel by thelcommutators 317 and 328. vAs state the up-drive magnet 310 will againbe energized in'position 7 and in View of the fact that relay-312 cannotoperate until a ground connection is encountered for Vits circuit atthis selector, the vupdrive magnet will continue to drive thebrushes'over the lower half of theterminal bank until .commutator 328-is reached by Athe commutator brushes 316. This takes lace at vtheVbeginning of the second half` o the bank and the circuit for therelay312 will now be'completed from battery over the tip conductor cam 303 inposition 7, winding of relay 312, cam 314, through the commutators ofthe group 313, brushes' 316 to ground at the commutator 328.

Ifground` had been connected to the tip conductor instead of battery thecircuit for relay 312 would have been completed as soon after the-brushselection as the brushes 316 of the -commutator had reached the lowergroup of cummutator segments 342. This circuit would have been completedfrom battery oam318 in position 7, commutator 317,

commutator 342, resistance' 315, cam 314, relay 312 and from there tothe ground on the tip conductor at cross connecting frame at 13. In thiscase the selection of the desired l private Vbranch exchange group oftrunks iso will have taken place in the lower half of the selected maingroup in the same manner as hereinafter described for the selection inthe upper half.

Depending now on the resistance condi".

tions at cross connecting frame between the tip conductor and thebattery at 13 relay 312 will operate when the proper circuit conditionshave been established. The up-drive magnet will therefore nowimmediately be stopped by the operation of relay 312, if the first groupof trunks are to be selected or continue to operate until the desiredgroup is selected as determined by the resistance condition in thecircuit for relay 312. As shown in the drawings the battery at 13 isconnected through one resistance unit to the tip conductor andconsequently the relay 312 will not operate until the second group hasbeen reached, that is until the first resistance unit 331 has beeneliminated from the circuit by the .brushes 316 coming in contact withthe second segment 332 of the upper group 330 .of commutator segments.The trunk huntincr following this selection will therefore ta (e placein the second group of the upper half of the bank selected by thetripped brushes.

When relay 312 operates causing relay 320 to operate the sequence switch308 will be advanced to position 8 over a circuit through cam 309. Inthis position the up-drive magnet will again operate over a circuitclosed by the operation of relay 334. This relay operates in position 71/1 over a circuit from battery, through its left-hand winding, cam 335to ground. Relay 334 is held operated through its right-hand windingthrough cam 337 to ground supplied at the sleeve terminals of busytrunks alternately with the ground supply through commutator 336. Thebrushes of the switch therefore advance over these busy trunks until anidle trunk is found when the holding ground for relay 334 is removedcausing it to release and stop the updrive magnet 310. The sequenceswitch 309 is now advanced to the ninth position from the circuitcompleted at the left-hand armature and back contact of relay 334 andcam 309 and a busy ground connection is placed on the sleeve through cam337.

In position 9 a circuit is closed for the operation of relay 250 in theauxiliary incoming selector 200 over cam 338. Relay 250 opens thecircuit for relay 29 in the incoming selector 1 and thereby causes thisrelay to release to connect the incoming `line 10 through. the repeatingcoil 30 to the tip and ring conductors extended to the auxiliary finalselector 300. It is evident that due to the release of relay 29 at thistime any suitable arrangement may be made to move the sequence switch 16for example to open the connections to leads 35 from the battery andground connections at thecross connecting frame 3, in fact the iinalselector may be entirely restored to normal at this time withoutinterference with the talking connection established from trunk 10 to atrunk to a private branch exchange.

Relay 339 is now operated over a circuit completed through the windingof relay 339, cams 303 and 304, armature and back contact of relay235winding of 238, cams 237 and 222, cams 32 and 33, armatures and backcontacts of relay 29, to ground and battery through the right-handwinding of repeating coil 30. Relay 339 in operating closes an obviouscircuit for relay 340. Relay 340 is held operated through a circuitcompleted through its inner lowe-r armature and front contact to batteryat cam 318. rlhe purpose of the operation of this relay will presentlybecome apparent. The connection is now completed from the incoming line10 through the auxiliary switches 200 and 300 to an idle trunk such as342 of the selected group and the ringing equipment (not shown) will beactuated to call the selected private branch exchange.

The called operator at this exchange may then answer the call and theconnection to the desired subscriber extended in the usual manner.

When disconnection is desired the opening of the connection over thetrunk 10 causes the release of the incoming and final selector in theusual manner. On the advance of the sequence switch 15 to normal theloop through the repeating coil 30 is opened causing the release ofrelay 339. lThe release of this relay closes a circuit for the advancingof the sequence switch 308 to position 18 over the circuit completed atthe lower outer armature and front contact of relay 340 and cam 309.

In this position 'the down-drive magnet 344 is operated from a circuitcompleted at cam 324 to return the switch 300 to normal position where acircuit is completed through commutator 345 to return the sequenceswitch 308 to normal position through cam 314. Auxiliary incomingselector 200 is returned to normal at the releasing of relay 238. Therelease of this relay causes the operation of relay 241 from batterysupplied at cam 203. Relay 239 was operated when the relay 238 'wasoperated and on the release of this relay,

relay 241 operates as hereinbefore described. The operation of relay 241now causes the sequence switch 203 to be advanced to position 18 over acircuit completed from battery, sequence switch 203, cam 251, outerrighthand armature and front contact of relay 241 to ground. Thedown-drive magnet 253 is now operated through the circuit completed atcam 217 and when the switch 200 has been returned to normal position acircuit is co1npleted through commutator 254 and cam 251 for the returnof the sequence switch 203 to normal position.

i It should be understood that while the invention has only beenillustrated in connection with a single system it may readily be appliedto a number of other arrangements without departing Jfrom thecspiritthereof.

What is claimed is:

l. In a telephone system, a calling line, groups ot lines, switchingmeans responsive to impulses received over said calling line for markinga group of lines, auxiliary switching means, and means responsive tosaid marking for directing said auxiliary switching means to select themarked group of lines and to connect the calling line with an idle linein the selected group.

2. In a telephone system, a calling line, a group of lines, switchingmeans responsive to impulses received over said calling line for markingsaid group of lines, auxiliary switching means, and means responsive tosaid marking for directing said auxiliary switching means to select themarked group of lines and to hunt for an idle line in said selectedgroup and to connect said calling line to an idle line in said selectedgroup when found.

3. In a telephone system, a calling line, called lines, groups of lines,switching means responsive to impulses received over the calling line,for selecting a called line, or for marking a group of lines, auxiliaryswitching means, means responsive to said marking for controlling saidauxiliary switching means to connect the calling line with an idle linein the marked group of lines over a pathv excluding said first mentionedswitching means.

4. In a telephone system, a calling line, groups of lines, switchingmeans responsive to impulses received over the calling line for markinga group of lines. auxiliary switching means, means responsive to saidmarking for controlling said auxiliary switching means to select themarked group and hunt for and connect said calling line with an idleline in the marked group over a path excluding said first mentionedswitching means.

5. In a telephone system, a calling line, groups of lines, a switch,means for selecting a certain set of terminals to said switch,representing a certain group of lines, another switch in which saidgroups of lines terminate, means responsive to the selection of saidsets of terminals for actuating said other switch to select a group ofterminals thereon corresponding to the group of lines represented by theselected terminals on said first mentioned switch, for hunting for theterminals of an idle line in said group and for connecting the callingline and said idle line exclusive of said first mentioned switch.

6. In a telephone system, a calling line, groups of lines, sets ofterminal points comprising various combinations of potentials andrepresenting particular groups of lines, means for selecting any set ofterminal points representing a particular group of lines, switchingmeans, means responsive to said selection for actuating said switchingmeans to connect the calling line with an idle line in the group oflines represented by the selected set of terminal points.

7. In a telephone system, al calling line, groups of lines, sets ofterminal points, connections from said sets to ground or battery throughvarious combinations of resistances, means for selecting any set ofterminals, switching means, means responsive to the selection of saidterminals for actuating said switching means to connect the calling lineto a particular group of lines corresponding to the characteristiccombination encountered at the selected set of terminals.

8. In a telephone system, a calling line, groups of lines, sets ofterminal points, connections from said sets to ground or battery throughvarious combinations of resistances, means for selecting any set ofterminals, a plurality of switches, means responsive to the electricalconditions encountered at certain of the terminals in a selected set forcontrollingrthe setting of certain of said switches and responsive tothe electrical conditions encountered at certain other terminals in theselected set for controlling the setting of other switches for theestablishmg of a connection from the calling line to a certaincorresponding group of lines.

In testimony whereof, I have signed my name to this specilication this6th day of February, 1930.

ARTHUR B. STERN

